JP3141169B2 - Sodium-sulfur battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sodium-sulfur battery, and more particularly, to a sodium-sulfur battery having an anode structure suitable for preventing battery damage and improving the life of the battery when the temperature is raised and lowered.

[0002]

2. Description of the Related Art A sodium-sulfur battery is provided with molten sodium as a cathode active material and molten sulfur or sodium polysulfide as an anode active material on one side through a solid electrolyte tube that allows only sodium ions to pass through. About 300 ~
A secondary battery that is charged and discharged at 350 ° C.

[0003] When the battery is cooled, a cylindrical anode structure in which a porous or fibrous electron conductive material is filled with sulfur as an anode active material is formed by melting solid sulfur or sodium polysulfide into a solid electrolyte tube. Although solidified while being in close contact with the outer circumference, sulfur or sodium polysulfide has a higher coefficient of thermal expansion than β ″ -alumina forming the solid electrolyte tube, that is, a large amount of shrinkage causes stress due to pinching of the solid electrolyte tube. At this time, if the contraction force acts uniformly over the entire circumference of the solid electrolyte tube, the circumferential stress on the solid electrolyte tube is compressed, and there is no problem in strength. These non-uniformities, such as uneven thickness of the anode structure, eccentricity of the solid electrolyte tube and the anode container, roundness of the solid electrolyte tube and unevenness of the density of the anode structure or uneven solidification rate, etc. To the solid electrolyte tube in the circumferential direction becomes non-uniform external forces act locally the tensile stress is generated which may lead to destruction of the entire battery due to the damage of the solid electrolyte tube of this part.

The anode structure is generally made by using carbon fiber felt as a porous electron conductive material and filling it with sulfur, and inserted between a solid electrolyte tube and an anode container. This is because sulfur does not have electron conductivity as a simple substance of sulfur, so the porous electron conductive material is filled in the anode, and the passage of electrons flowing into the anode container from the external circuit or flowing out from the external circuit to the inside of the anode is performed. Is provided. At this time, the carbon fiber felt is held by solidification of sulfur while being compressed in the radial direction. This is to improve the contact between the anode container as the external terminal and the carbon fiber in the operating state of the battery in which the sulfur is melted, and to improve the electron conductivity by increasing the filling rate of the carbon fiber in the anode. It is.

[0005] In order to reduce the external force generated from the anode structure and reduce the stress of the solid electrolyte tube, a conventional method of dividing the anode structure into a structure as disclosed in JP-A-61-156640.
Measures such as cutting and crushing are taken. Further, as another conventional example, a metal material whose surface is sulfided is provided around a solid electrolyte tube (Japanese Patent Application Laid-Open No. 60-235369), and a metal material whose surface is sulfided is provided with an annular support member at the bottom of the solid electrolyte tube. JP-A-62-82668).

[0006]

However, even if the anode structure is divided or cut in the prior art, the separated fibers in the initial assembly state are restored when the sulfur is melted, and the fibers are re-crossed. As a result, there is no gap, and the effect of reducing stress cannot be expected. further,
Even if the anode structure is made of only sulfur without carbon fiber,
Since it has been confirmed that an external force is generated by solidification, it is impossible to avoid stress generated in the solid electrolyte tube at the time of solidification of the anode structure, and prevention of initial damage and improvement of life cannot be expected.

To explain this point in more detail, the anode structure has a structure like a so-called fiber reinforced resin in which sulfur or sodium polysulfide is filled in a porous or fibrous electron conductive material. This anode structure is filled with sulfur or sodium polysulfide at a density of about 90% or more on average, and therefore, the thermal expansion coefficient when solidified depends on the physical properties of the sulfur or sodium polysulfide. For example, the coefficient of thermal expansion from room temperature to about 100 ° C. is about 5 to 10 × 1 of β ″ -alumina forming the solid electrolyte tube.
It is as large as about 30 to 200 × 10 to ⁶ ° C. compared to 0 to ⁶ ° C. That is, when the temperature is lowered, the heat shrinkage of the anode structure is larger than that of the solid electrolyte tube. Therefore, all the contraction force acts on the solid electrolyte tube as a circumferential nonuniform compressive force. At this time, the solid electrolyte is irregularly deformed as shown in FIG. 6 due to the above-mentioned structural non-uniformity or the non-uniform density of the anode structure and the external force generated by the temperature distribution. Due to this deformation, a tensile stress is generated in a circumferential direction on the outer peripheral side at a place where the deformation curvature is large, for example, at point A, and when the generated stress reaches or exceeds the strength of the solid electrolyte tube, the solid electrolyte tube is broken. It should be noted that the external force generated from the anode structure cannot be completely eliminated even in the above-mentioned conventional technology, and the solid electrolyte tube side is also a ceramic structure, so that there is a limit to the increase in strength or variation. When the high stress generating portion and the low strength member are combined, breakage occurs relatively early, so that it is necessary to disperse the external force by a method different from the conventional method. The metal material disclosed in JP-A-60-235369 is provided to increase the utilization of the anode active material, and is not considered at all for the stress of the present invention. The annular support member disclosed in Japanese Patent Application Laid-Open No. 62-82668 prevents the lateral displacement of the electrolyte tube, and does not consider the stress of the present invention at all.

[0008] An object of the present invention is to provide a sodium-sulfur battery in which the stress generated in the solid electrolyte tube is reduced to prevent the battery from being damaged and to improve the life thereof, in order to solve the above problems. .

[0009]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides sodium as a cathode active material inside a bag-shaped solid electrolyte tube, and a porous or fibrous electron conductive material outside the solid electrolyte tube. In a sodium-sulfur battery in which a cylindrical anode structure filled with sulfur as an anode active material is disposed, a material is disposed between the outer surface of the solid electrolyte tube and the anode structure. A stress dispersing member for dispersing the stress by receiving a stress applied to the solid electrolyte tube is provided.

[0010]

In the above-mentioned sodium-sulfur battery, the stress dispersion member is preferably a sleeve provided on the outer surface of the solid electrolyte tube. The sleeve is preferably provided with a clearance fit on the outer surface of the solid electrolyte tube. Also,
The sleeve is preferably provided with a hole for ensuring contact between the anode structure and the solid electrolyte tube. Further, the anode structure is preferably divided into a plurality of parts in the axial direction, and the sleeve is preferably a sleeve with a flange provided on the overlapped portion of the divided individual anode structures. The anode structure is preferably divided into a plurality of parts in the axial direction, and the sleeve is preferably a short sleeve provided on each of the divided anode structures.

[0012]

[Function] To reduce the stress generated in the solid electrolyte tube, the diameter of the solid electrolyte tube can be reduced, or conversely, the thickness of the anode structure can be reduced to make the solid electrolyte tube thicker. (Capacity, efficiency) is not preferred. Therefore, in order to reduce the stress of the solid electrolyte tube while maintaining the battery performance, a stress dispersing member such as a sleeve material for protecting the solid electrolyte tube is required.

According to the present invention, the external force generated from the anode structure is borne by a stress dispersing member such as a sleeve inserted into the outer periphery of the solid electrolyte tube by a clearance fit or the like.
The sleeve or the like must have such a rigidity that the plastic does not easily deform plastically against the external force. Here, assuming that the plate thickness of the solid electrolyte tube is Tmm, the required rigidity of the sleeve depends on the intended amount of stress reduction, but it is empirically desirable that the equivalent plate thickness be T / 2 or more. When an experiment was performed on a test sample having a plate thickness of 2 mm of the solid electrolyte tube, a stress of about 100 MPa was actually measured at point A in FIG. This 100
In order to reduce the MPa to 50 MPa, half of the external force from the anode structure has to be received by the sleeve, and the required thickness is 1 mm. Therefore, when the punched portion or the non-inserted portion is taken into consideration, the equivalent plate thickness becomes T / 2 or more.

However, when the entire outer periphery of the solid electrolyte tube is covered with a sleeve or the like, the contact between the solid electrolyte tube and the carbon fiber felt as the electron conductive material is interrupted or only the local contact is made. As a result, the battery does not hold. Therefore, a substantial area of the total surface area of the solid electrolyte tube needs to be in contact with the solid electrolyte tube and the electron conductive material. For this purpose, the sleeve or the like has a long cylindrical structure made of a punched plate, or covers only a necessary length with the sleeve, and the other part is a single piece for contacting the solid electrolyte tube and the electron conductive material without a shield. It is necessary to have a plurality of ring-shaped short sleeve structures.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a sodium-sulfur battery according to the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. Molten sodium 1, which is a cathode active material, is inside solid electrolyte tube 2, and its upper part is sealed by cathode container 3, which is also an external terminal. As described above, the sulfur as the anode active material is inside the anode structure 4 in a state of being filled in the carbon fiber felt, and is wrapped in the anode container 5 which is also an external terminal. The insulating ring 6 is an electrical insulator between the cathode container 3 and the anode container 5. In the present invention, a sleeve 7 as a stress dispersing member is provided on the outer periphery of the solid electrolyte tube 2, that is, inside the anode structure 4.

The operation of the thus constructed embodiment will be described below. The sleeve 7 may be molded at the same time as carbon fiber and sulfur when the anode structure 4 is molded,
It is either assembled by itself or assembled. The anode structure 4 compresses a carbon fiber having a material thickness larger than the gap between the inner diameter of the anode container 5 and the outer shape of the solid electrolyte tube 2 to mold sulfur, and forms a cylindrical or segment structure. Therefore, the solid electrolyte tube 2 and the sleeve 7 and
The gap between the sleeve 7 and the anode structure 4 is a clearance fit in the initial assembly state. However, when the sulfur filled in the anode structure 4 is melted by the first heating, the carbon fibers are compressed as described above. The state is released, and is maintained in a stretched state between the anode container 5 and the sleeve 7 by the restoring force. In this case, the stress generated in the solid electrolyte tube 2 due to the restoring force is about 0.1 MPa, which is not a magnitude that causes a problem in strength. On the other hand, when the temperature is lowered, the range from the operating temperature of the sodium-sulfur battery of about 300 to 350 ° C. to the melting point of sulfur of about 120 ° C. is the liquid phase, but it is solidified by the subsequent cooling and accordingly the anode structure 4 Shrink while increasing in strength. In the case of the conventional structure, all of the contraction force is received only by the solid electrolyte tube 2, but the present invention also takes over the contraction force by the sleeve 7.

FIG. 2 shows in detail a long sleeve provided with a hole 8 as an example of the structure of the sleeve 7. It is necessary that the sleeve 7 has a strength that does not cause plastic deformation due to an external force at the time of thermal deformation of the anode structure 4, and a punched hole 8 is provided to secure a contact portion.

FIG. 3 shows a short sleeve structure with a flange as another embodiment of the present invention. According to the present embodiment, the anode structure 4 is divided into two or more anode structures 4 in the axial direction, and a sleeve 9 with a flange is provided at the overlapping portion, whereby an external force generated from the anode structure 4 is reduced. The solid electrolyte tube 2 and the anode structure 4 are in contact with each other except for the sleeve 9 with the flange, so that the battery performance is ensured.

FIG. 4 shows a storage device as another embodiment of the present invention.
3 shows a structure in which a plurality of short sleeves 10 are arranged along the solid electrolyte tube 2, and the function thereof is the same as that of FIG.

FIG. 5 shows the relationship between the temperature and the stress generated in the solid electrolyte tube for the conventional structure and the present invention. In other words, the anode structure is hardened as the temperature decreases, and the strength also increases with the hardening, so that restraint stress is generated. If the stress exceeds the strength of the solid electrolyte tube, the solid electrolyte tube may be damaged. However, according to the present invention, the stress of the solid electrolyte tube is reduced, so that the battery can be prevented from being damaged and the life can be improved. Here, as shown in FIG. 3, an external force acts directly on the solid electrolyte tube 2 in a portion where the solid electrolyte tube 2 and the anode structure 4 are completely in contact with each other in the circumferential direction, but an adjacent sleeve applies the external force. The stress is reduced because of the burden.

Although the embodiments of the long and short sleeve structures having punched holes have been described above, the sleeve length may be set only for the portion where the solid electrolyte tube is desired to be protected. Sulfur or sodium polysulfide forming the anode structure is highly corrosive and has an operating temperature of about 300 to 350 ° C., so that the material for forming each of the sleeves is ceramic or stainless steel (SUS). ) Must have corrosion resistance.

As described above, according to the present embodiment, the external force caused by the thermal deformation of the anode structure at the time of raising and lowering the temperature is shared by the stress dispersing member disposed on the outer periphery of the solid electrolyte tube, so that the solid electrolyte tube can be used. The generated stress can be reduced, and breakage of the solid electrolyte tube during temperature rise / fall can be prevented.

[0023]

According to the present invention, the external force caused by the thermal deformation of the anode structure, which has been conventionally received only by the solid electrolyte tube, is shared by the stress dispersing member disposed on the outer periphery of the solid electrolyte tube. It is possible to reduce the stress generated in the tube, thereby preventing damage at the time of temperature rise and fall, and realizing a highly reliable sodium-sulfur battery.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is an assembled state diagram relating to FIG. 1;

FIG. 3 is a partial cross-sectional view showing another embodiment of the present invention.

FIG. 4 is a partial sectional view showing another embodiment of the present invention.

FIG. 5 is a stress state diagram of a conventional solid electrolyte tube of the present invention.

FIG. 6 is a cross-sectional view illustrating a defect of a conventional example.

[Explanation of symbols]

 2 solid electrolyte tube 4 anode structure 7 sleeve (stress dispersing member) 8 punched hole 9 flanged sleeve 10 short sleeve

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-U 3-77369 (JP, U) (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01M 10/39

Claims (5)

(57) [Claims] 1. A cylindrical solid electrolyte tube in which sodium as a cathode active material is filled inside a bag-shaped solid electrolyte tube, and a porous or fibrous electronic conductive material is filled with sulfur as an anode active material outside the solid electrolyte tube. In a sodium-sulfur battery provided with an anode structure, a stress applied to the solid electrolyte tube from the anode structure between the outer surface of the solid electrolyte tube and the anode structure disperses the stress. A stress distribution member is provided , and the stress distribution member is provided on an outer surface of the solid electrolyte tube.
The sleeve is divided into a plurality in the axial direction.
With flanges provided at the overlap of individual anode structures
A sodium-sulfur battery, wherein the battery is a sleeve . 2. A cathode active material is provided inside a bag-shaped solid electrolyte tube.
Is a porous or porous material outside the solid electrolyte tube.
Fills a fibrous electron conductive material with sulfur, which is the anode active material.
Sodium-sulfur containing a cylindrical anode structure
In the yellow battery, the outer surface of the solid electrolyte tube and the anode structure
Between the anode structure and the solid electrolyte tube
A stress dispersing member for dispersing the stress upon receiving the stress is provided.
The stress dispersion member is provided on an outer surface of the solid electrolyte tube.
The sleeve is divided into several parts in the axial direction.
And a short sleeve provided on each anode structure . 3. The sleeve according to claim 1, wherein
Of the solid electrolyte tube is equal to or more than １ ／ of the plate thickness of the solid electrolyte tube.
Sulfur battery - sodium, characterized in that that. 4. The sodium-sulfur battery according to claim 3, wherein the sleeve is provided with a clearance fit on the outer surface of the solid electrolyte tube. 5. The sodium-sulfur battery according to claim 3, wherein the sleeve is provided with a hole for ensuring contact between the anode structure and the solid electrolyte tube.